This invention relates to identification friend-or-foe (IFF) systems and, more particularly, to a laser vibrometer IFF system.
As is well-known, laser beams have a high spatial and temporal coherence. One advantage of this is that it allows them to be used for very sensitive range measurements. This is done using interferometry principles. Using certain interferometric techniques, it is now possible to very precisely measure the velocity profile, for example, of air molecules around a ship's hull.
Recent advances in the development of compact, solid state lasers have made the use of velocimeters such as noted above quite practical for use in a number of applications. In the military area, one application heretofore not considered is the use of a laser based velocimeter to measure the vibration signature of different vehicles. As a practical matter, it would be advantageous to be able to identify a vehicle, plane, ship, or other object as being either a friend or an enemy using this technique. The advantage would lie in being able to establish a vibration signature for each thing likely to be encountered in a combat environment. If the signatures of all objects cannot be ascertained, certainly those of friendly forces can be. Thereafter, when an object is to be queried to determine its status, it vibration signature is first obtained. This is then compared against all available signatures. If the signature matches a known friendly signature, the object is treated accordingly. If the signature matches that for a foe, appropriate steps to neutralize the threat it represents can be taken. If there is no match, it indicates that other identification measures should be undertaken.
In addition to the ability to readily identify objects, another advantage of such a system would be its covertness. Since the querying platform both interrogates the target and evaluates the response, and because there is nothing required of the target to obtain its response, the target, if friendly, does not expose itself by transmitting a response message to a received query. Thus, the system allows the target to be totally passive, or non-cooperative.